Electrophotographic developing device

ABSTRACT

An electrophotographic developing device comprising an electroconductive endless belt driven in a substantially horizontal plane, means for forwarding a flexible electrophotographic sensitive material carrying thereon an electrostatic latent image onto the upper surface of the endless belt at substantially the same speed and in the same direction as the belt, and a means for supplying a liquid developing agent to the opening between the endless belt and the electrophotographic sensitive material so that the liquid developing agent is retained between the endless belt and the electrophotographic sensitive material and conveyed therebetween so that the agent develops the electrostatic latent image on the electrophotographic sensitive material.

United States Patent [191 Fukushima et al.

[111 3,804,062 [451 Apr. 16, 1974 [75] Inventors: Osamu Fukushima; Masamichi Sato,

both of Asaka, Japan [73] Assignee: Fuji Photo Film Co., Ltd.,

Kanagawa, Japan [22] Filed: Nov. 27, 1970 [21] Appl. No.: 92,976

[30] Foreign Application Priority Data Nov. 27, 1969 Japan 44-95222 [52] US. Cl 118/637, 117/37 LE, 118/D1G. 23 [51] Int. Cl G03g 13/00 [581 Field of Search 118/637, DIG. 23; 117/37 LE; 95/94 G [56] References Cited UNITED STATES PATENTS 3,669,073 6/1972 Savit et a]. 118/637 3,687,708 8/1972 Miller 117/37 LE 3,367,791 2/1968 Lein....., 117/37 3,308,737 3/1967 Susumu Fukuda 95/89 3,556,050 l/1971 Trachtenberg 118/637 3,363,530 l/l968 Rice 95/89 3,592,678 7/1971 l-lonjo et al.... 117/37 3,192,846 7/1965 Wright 95/94 2,431,041 11/1947 Hassler 95/89 3,247,825 4/1966 Johnson 118/637 3,566,834 3/1971 Tamai et al 118/637 3,570,456 3/1971 Dahlquist 118/637 OTHER PUBLICATIONS Liquid Crystal Electrophotographic Display by R. Keyes, IBM Digest, Vol. 12, No. 12, May 1970.

Primary ExaminerMervin Stein Assistant Examiner-Leo Millstein Attorney, Agent, or Firm-J. T. Martin; Gerald J. Ferguson, Jr.; Joseph J. Baker [57] ABSTRACT An electrophotographic developing device comprising an electroconductive endless belt driven in a substantially horizontal plane, means for forwarding a flexible electrophotographic sensitive material carrying thereon an electrostatic latent image onto the upper surface of the endless belt at substantially the same speed and in the same direction as the belt, and a means for supplying a liquid developing agent to the opening between the endless belt and the electrophotographic sensitive material so that the liquid developing agent is retained between the endless belt and the electrophotographic sensitive material and conveyed therebetween so that the agent develops the electrostatic latent image on the electrophotographic sensitive material.

3 Claims, 6 DrawingFigures PATENTEDAPR 16 1974 SHEEY 1 0F 2 N GE mow

INVENTORS.

OSAMU FUKUSHIMA MASAMICHI SATO BY My ATTORNEY PATENTEDAPR 1 1914 3504.062

SHEEY 2 0F 2 PEG. 3

INVENTORS, OSAMU FUKUSHIMA MASAMICHI SATO BY/QW/ ELECTROPHOTOGRAPI-IIC DEVELOPING DEVICE BRIEF EXPLANATION OF THE DRAWING FIG. 1 and FIG. 2 are schematic diagrams showing conventional typical developing methods, FIG. 3, FIG. 4, and FIG. 6 are side elevations in longitudinal section of the developing device according to the present invention, and FIG. is an oblique diagram showing one example of the endless belt to be used for the device of this invention.

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a liquid developing device for electrophotography. More particularly, it relates to a developing device which is suitable for high-speed development and unproductive of streaking of image.

The speed at which the electrostatic latent image is developed has reached the level of several tens of cm per second in the case of document copying. However, the speed for the development of images of continuous gradation and half-tone is far much lower so far as the present status of affairs stands.

An effort to increase the speed of development with the conventional device entails various difficulties. The first difficulty is encountered in the fact that reduced developing period fails to provide sufficient developing density and tends to produce the phenomenon of edge effect. This shortcoming is particularly conspicuous in case of the reproduction of images of continuous gradation. Elimination of this shortcoming calls for a certain extent of elongation of the developing time. The second difficulty is found in the phenomenon that increased developing speed results in the formation of a streaking in the developed image like the tail which follows a flying comet. Although what causes this phenomenon has not been clarified definitely, it has been learnt that the phenomenon fails to occur where the relative speed between the latent image surface and the developing liquid is small. In order for this difficulty to be overcome. it is necessary to minimize the relative speed occurring between the latent image surface and the developing liquid in the direction parallel to the latent image surface.

The present invention concerns a liquid developing device for electrostatic latent images, enjoying freedom from these shortcomings.

FIG. 1 illustrates a conventional manual method employed typically for developing images of continuous gradation. In this device, the sheet 11 carrying a latent image thereon is disposed so as to allow the latent image plane to confront the developing electrode 12, with the liquid developing agent supplied to the opening between the sheet 11 and the developing electrode 12. The liquid developing agent 14 is held in the container 13 and is allowed to flow down the opening 15 through gravitational pull. While the agent flows down the opening 15, the latent image is developed thereby. Thereafter, the agent is received in the container 16. In accordance with such method as this, since the liquid developing agent flows along the latent image surface, the developed image forms a streak in the direction in which the agent flows down. Such an image is quite unsightly and fails to provide an image of high quality.

FIG. 2 illustrates an example of the developing device which produces no relative speed between the latent image surface and the developing liquid and, consequently, produces no streak in the developed image. In the device of FIG. 2, the metallic drum 21 rotates in the direction indicated by the arrow mark 23 and the lower portion of the drum is kept submerged in the developing liquid 25 which is held in the container 24. The drum 21 has a film of the developing agent formed on its surface as its lower portion comes into contact with the developing liquid and carries the film upward as it rotates. On the upper portion of the drum 21, the latent image sheet 11 advances in the direction indicated by the arrow mark 22, with the latent image surface looking downward. Thus, the latent image surface is brought into contact with the film of the liquid. The drum 21 also serves as the developing electrode. When the tangential speed of the drum 21 is so selected as to substantially equal the speed of the sheet 11, the relative speed between the latent image surface and the liquid developing agent will become very small, making it possible to preclude the formation of streak in the developed image. In the device like that of FIG. 2, however, since the time during which the latent image surface is held in contact with the liquid developing agent is so short that it is difficult to obtain sufficient developing density. Where a low developing speed suffices, a rather satisfactory image may be obtained by using a liquid developing agent having high toner concentration and high viscosity. When the liquid developing agent has high concentration and high viscosity, the smearing of the latent image surface by the agent becomes conspicuous and the preventive measure therefor becomes complicated. If there is used a liquid developing agent having low concentration and low viscosity, the agent adhering to the drum surface and being scooped up toward the highest point of the drum flows down along the drum surface because of gravitational pull. As a consequence, the amount of toner to be brought into contact with the latent image surface will be insufficient. Thus, the required developing density'cannot be obtained no matter how low the developing speed may be fixed.

The present invention provides a developing device which permits the development of image to be accomplished at a high speed without having to use a developing liquid with high concentration and high viscosity, with the developed image free from the phenomenon of streaking.

FIG. 3 is a schematic cross section of one preferred embodiment of the present invention. In the diagram of FIG. 3, 301 denotes a flexible endless belt at least one surface of which is electroconductive, and this belt is revolved along two rollers 302 and 303. Concrete examples of the endless belt to be used are an endlessly shaped strip of plastic film having the surface thereof plated or vacuum deposited with a metallic substance, an electroconductive rubber belt, and a flexible metallic belt. The endless belt is driven at a fixed speed in the direction indicated by the arrow mark 317. Onto the endless belt in the neighborhood of the roller 302, the liquid developing agent 307 held in the container 306 is scooped up by the pump 304. The liquid developing agent can be supplied uniformly onto the endless belt by shaping the discharge portion 305 of the pump in the form of a slit or of a series of small orifices. The liquid developing agent which has been placed on the endless belt forms a flat, smooth film and, in that state, advances to the right together with the belt. While the liquid developing agent in practically a fixed film thickness is forwarded at practically a constant speed toward right, the sheet 308 which contains a latent image is sent between the pinch rollers 309 and 310 and then forwarded from upper left toward the endless belt surface at a certain angle with reference to the belt surface (which is virtually horizontal) at substantially the same speed as the driving speed of the endless belt. The forward end of the sheet comes into contact with the surface of the endless belt slight to the right (forward) of the discharge portion 305 of the pump. Since the sheet is flexible, it begins to advance practically parallelly with the endless belt from that point of contact. Since the liquid developing agent is supplied at a fixed rate onto the endless belt before the sheet comes to confront the endless belt across a narrow opening, there is formed substantially a uniform depth ofliquid developing agent in the opening between the endless belt surface and the latent image surface. Further, the sheet and the endless belt are made to advance at practically the same speed while keeping the said layer of liquid. Consequently no streaking occurs in the developed image. Moreover, the time during which the latent image surface is held to confront the endless belt may be lengthened as desired by suitably selecting the length of the belt. The endless belt serves as the developing electrode and, at the same time, as the carrier of the sheet. The required developing density can be obtained easily by suitably selecting the toner concentration of the liquid developing agent. This is because, unlike the device shown in FIG. 2, this device does not suffer the liquid developing agent to flow down gravitationally. The sheet which has undergone the step of development is passed between a pair of squeezing rollers 312 and 313 so as to be freed of the excess liquid developing agent adhering to the latent image surface. The liquid developing agent which is remaining on the endless belt may he recovered in the container 306 so as to be put to reuse or it may be received in a separate container 315. To receive it in the container 315, the liquid on the endless belt may be scraped out by means of a brush 314 or it may be removed by some other suitable device. Since the liquid 316 has a smaller toner concentration than the liquid developing agent 307, it may be discarded. The liquid which has been removed by the squeezing rollers is likewise received in the container 315. It is effective for the elimination of fogging to wash, by a suitable method, the developed sheet prior to the step of squeezing, though not illustrated in FIG. 3. It is desirable that the pinch roller 310 is highly insulative and that either of the pair of pinch rollers 309 and 310 is made of a flexible substance. For effective prevention of the image from fogging, the pinch roller 310 is desired to be coated with such porous material as sponge and impregnated with a highly insulative liquid, so that it will uniformly wet the latent image surface as the sheet passes the rollers (by way of prebath). For the sheet to keep a uniform space across the liquid developing agent from the endless belt surface, it is effective to have the blower 311 supply a current of air downward against the sheet. This method proves particularly important where the sheet is liable to curl or it is made of a paper of considerable thickness. This method is not required where the sheet is flat and smooth and is supple.

FIG. 4 shows another preferred embodiment of the present invention. The only difference between the device of FIG. 4 and that of FIG. 3 resides in the manner of supplying the liquid developing agent onto the endless belt. In the device of FIG. 4, the supply roll 401 is used in the place of the pump. This supply roll is so disposed that the lower portion thereof is kept submerged in the liquid developing agent. When it is rotated at a suitable speed, the liquid developing agent is allowed to adhere to the surface thereof and then scooped up. When the liquid reaches the neighborhood of the top portion thereof, the doctor blade 403 scrapes the liquid off the surface. The liquid which has been scraped by the blade flows over the blade and reaches the endless belt. The same performance as the pump may be obtained by suitably selecting the revolution number of the supply roll and the shape of the doctor blade.

In addition to the preceding manners of supplying the liquid developing agent onto the endless belt, the liquid developing agent may be supplied gravitationally from a tank positioned at an elevated level through a pipe onto the endless belt surface. Briefly speaking, the spirit of the present invention resides in allowing a suffleient amount of liquid developing agent to be mounted on the endless belt by a suitable method without permitting the liquid to flow down the belt, causing the latent image surface to confront the belt from thereabove and, at the same time, driving the latent image surface, the liquid developing agent and the endless belt (serving as the developing electrode) at substantially the same speed.

FIG. 5 shows one form of the endless belt 301 to be used for the present invention. The numeral 501 denotes the portion where the liquid developing agent is mounted in a uniform depth and made to confront the latent image surface. The numeral 502 denotes an endless embankment provided along the edge of belt so as to prevent the liquid developing agent from falling off the side of belt. By incorporation of this means, sufficient amount of liquid developing agent can be held uniformly on the endless belt 501. From the characteristics of the present invention, the surface of the end less belt 501 is desired to be flat and smooth. lncorporation of meshes in the belt is not desirable from the standpoint of keeping the liquid in position. As concerns the shape of this endless belt, it is permissible to employ an endless belt which is formed by overlaying an endless belt of metallic gauze or fabric material with a plastic endless belt which has the surface thereof plated or vacuum deposited with metallic substance or coated with an electroconductive paint. The materials used for the endless belt are required to be resistant to the corrosive action of the liquid developing agent. Where plastic materials and rubber are used, attention must be paid to fulfilling this requirement.

In the endless belt, the electroconductive layer is not always required to appear on the surface. The electroconductive surface may be covered with a highly insulative liquid retaining material. For example fibers may be planted electrostatically densely to a depth of a small fraction of 1 mm up to 1 mm. Or, a porous layer of velvet, flannel, or sponge may be pased on the surface. Incorporation of such a liquid-retaining material serves to improve the retention of the liquid developing agent on the endless belt, making it possible to lower the concentration of liquid developing agent. It also serves to keep uniform the opening between the electrostatic latent image surface and the electroconductive portion of the endless belt.

FIG. 6 shows an example of the device using a plurality of endless belts. In the diagram, 601 denotes a sheet holding an electrostatic latent image on the lower surface thereof, 602 a porous roller for providing prebath to the sheet 601, 602 and 603 a pair of pinch rollers, 604, 606 and 608 endless belts, 605, 607 and 609 rollers for holding the sheet against the upper surface of the endless belt, and 610 through 612 discharge portions for supplying the liquid developing agent onto the endless belts. The numerals 613 and 614 denote sponges for wiping the liquid developing agent away the endless belts. In this device, supply and replacement of the liquid developing agent is accomplished advantageously to afford images of uniform image quality.

By the device of this invention mentioned above, there can be obtained an image of sufficient density free from the phenomena of edge effect and streaking.

What is claimed is: 1. An electrophotographic developing device comprising an endless belt disposed about at least two rollers, at

least the surface of said belt being electroconductive; means for driving said belt at a predetermined speed;

means for supplying liquid developer onto said endless belt to form a film of said liquid developer on said belt, the inclination of said belt being such that said liquid developer does not flow down said belt but rather is carried along at said predetermined speed, said means for supplying the liquid developer including a supply roll partially disposed in a container of said liquid developer; means for rotating said supply roll to raise said developer liquid along the surface of said roll; and a plate having one end disposed adjacent said roll for removing said developer liquid therefrom and the other end thereof disposed over said endless belt so that the liquid developer removed from said roll flows over said endless belt to form said film; and

means for feeding a flexible electrophotographic sensitive material having an electrostatic latent image onto said film of liquid developer at substantially said predetermined speed and in the same direction as said belt so that said liquid developer is retained between said sensitive material and said endless belt whereby said latent image can be developed by liquid developer (1) in a short period of time without using a liquid developer of high concentration and low viscosity and (2) with minimal formation of the v edge effect in half tone and continuous tone images because (a) there is minimal relative movement between the liquid developer and the electrophotographic sensitive material and (b) the liquid developer is held in contact with the sensitive material for a relatively long time proportional to the length of the endless belt.

2. An electrophotographic developing device comprising an endless belt disposed about at least two rollers, at

least the surface of said belt being electroconductive;

means for driving said belt at a predetermined speed means for supplying liquid developer onto said enda less belt to form a film of said liquid developer on said belt, the inclination of said belt being such that said liquid developer does not flow down said belt but rather is carried along at said predetermined speed;

means for feeding a flexible electrophotographic sensitive material having an electrostatic latent image onto said film of liquid developer at substantially said predetermined speed and in the same direction as said belt so that said liquid developer is retained between said sensitive material and said endless belt;

means for blowing air downwardly on the top of said sensitive material as it passes said endless belt so that whenever said sensitive material is very thick or tends to cure, the distance between said sensitive material and said endless belt is maintained substantially uniform; and

whereby said latent image can be developed by liquid developer 1) in a short period of time without using a liquid developer of high concentration and low viscosity and (2) with minimal formation of the edge effect in half tone and continuous tone images because (a) there is minimal relative movement between the liquid developer and the electrophotographic sensitive material and (b) the liquid developer is held in contact with the sensitive material for a relatively long time proportional to the length of the endless belt.

3. An electrophotographic developing device comprising and endless belt disposed about at least two rollers,

at least the surface of said belt being electroconductive, said endless belt including raised portions disposed along the sides thereof to retain said liquid developer thereon;

means for driving said belt at a predetermined speed;

means for supplying liquid developer onto said endless belt to form a film of said liquid developer on said belt, the inclination of said belt being such that said liquid developer does not flow down said belt but rather is carried along at said predetermined speed; and v means for feeding a flexible electrophotographic sensitive material having an electrostatic latent image onto said film of liquid developer at substantially said predetermined speed and in the same direction as said belt so that said liquid developer is retained between said sensitive material and said endless belt whereby said latent image can be developed by liquid developer'(l) in a short period of time without using aliquid developer of high concentration and low viscosity and (2) with minimal formation of the edge effect in half tone and continuous tone images because (a) there is minimal relative movement between the liquid developer and the electrophotographic sensitive material and (b) the liquid developer is held in contact with the sensitive material for a relatively long time proportional to the length of the endless belt. 

1. An electrophotographic developing device comprising an endless belt disposed about at least two rollers, at least the surface of said belt being electroconductive; means for driving said belt at a predetermined speed; means for supplying liquid developer onto said endless belt to form a film of said liquid developer on said belt, the inclination of said belt being such that said liquid developer does not flow down said belt but rather is carried along at said predetermined speed, said means for supplying the liquid developer including a supply roll partially disposed in a container of said liquid developer; means for rotating said supply roll to raise said developer liquid along the surface of said roll; and a plate having one end disposed adjacent said roll for removing said developer liquid therefrom and the other end thereof disposed over said endless belt so that the liquid developer removed from said roll flows over said endless belt to form said film; and means for feeding a flexible electrophotographic sensitive material having an electrostatic latent image onto said film of liquid developer at substantially said predetermined speed and in the same direction as said belt so that said liquid developer is retained between said sensitive material and said endless belt whereby said latent image can be developed by liquid developer (1) in a short period of time without using a liquid developer of high concentration and low viscosity and (2) with minimal formation of the edge effect in half tone and continuous tone images because (a) there is minimal relative movement between the liquid developer and the electrophotographic sensitive material and (b) the liquid developer is held in contact with the sensitive material for a relatively long time proportional to the length of the endless belt.
 2. An electrophotographic developing device comprising an endless belt disposed about at least two rollers, at least the surface of said belt being electroconductive; means for driving said belt at a predetermined speed; means for supplying liquid developer onto said endless belt to form a film of said liquid developer on said belt, the inclination of said belt being such that said liquid developer does not flow down said belt but rather is carried along at said predetermined speed; means for feeding a flexible electrophotographic sensitive material having an electrostatic latent image onto said film of liquid developer at substantially said predetermined speed and in the same direction as said belt so that said liquid developer is retained between said sensitive material and said endless belt; means for blowing air downwardly on the top of said sensitive material as it passes said endless belt so that whenever said sensitive material is very thick or tends to cure, the distance between said sensitive material and said endless belt is maintained substantially uniform; and whereby said latent image can be developed by liquid developer (1) in a short period of time without using a liquid developer of high concentration and low viscosity and (2) with minimal formation of the edge effect in half tone and continuous tone imaGes because (a) there is minimal relative movement between the liquid developer and the electrophotographic sensitive material and (b) the liquid developer is held in contact with the sensitive material for a relatively long time proportional to the length of the endless belt.
 3. An electrophotographic developing device comprising and endless belt disposed about at least two rollers, at least the surface of said belt being electroconductive, said endless belt including raised portions disposed along the sides thereof to retain said liquid developer thereon; means for driving said belt at a predetermined speed; means for supplying liquid developer onto said endless belt to form a film of said liquid developer on said belt, the inclination of said belt being such that said liquid developer does not flow down said belt but rather is carried along at said predetermined speed; and means for feeding a flexible electrophotographic sensitive material having an electrostatic latent image onto said film of liquid developer at substantially said predetermined speed and in the same direction as said belt so that said liquid developer is retained between said sensitive material and said endless belt whereby said latent image can be developed by liquid developer (1) in a short period of time without using a liquid developer of high concentration and low viscosity and (2) with minimal formation of the edge effect in half tone and continuous tone images because (a) there is minimal relative movement between the liquid developer and the electrophotographic sensitive material and (b) the liquid developer is held in contact with the sensitive material for a relatively long time proportional to the length of the endless belt. 